This application relates to modulation of light and other optical applications based on optical whispering-gallery-mode (“WGM”) resonators.
Optical modulation is widely used in various applications such as optical communication and signal processing where light is modulated to carry certain information. Light may be modulated in amplitude or in phase. Electro-optical materials changes their refractive indices in response to applied electrical fields and hence may be used to modulate light.
Optical modulation may be implemented in WGM resonators. Examples for implementing optical modulation in WGM resonators may be found, e.g., U.S. Pat. No. 6,473,218. A dielectric material may be shaped to form a WGM resonator which supports a special set of resonator modes known as whispering gallery (“WG”) modes. These modes represent optical fields confined in an interior region close to the surface of the resonator due to the total internal reflection at the boundary. Microspheres with diameters from few tens of microns to several hundreds of microns have been used to form compact optical WGM resonators. Such spherical resonators include at least a portion of the sphere that comprises the sphere's equator. The resonator dimension is generally much larger than the wavelength of light so that the optical loss due to the finite curvature of the resonators is small. As a result, a high quality factor, Q, may be achieved in such resonators. Some microspheres with sub-millimeter dimensions have been demonstrated to exhibit very high quality factors for light waves, ranging from 1000 to 109 for quartz microspheres. Hence, optical energy, once coupled into a whispering gallery mode, can circulate within the WGM resonator with a long photon life time.
Such high Q values are generally difficult and expensive to obtain in conventional Fabry-Perot optical resonators formed with mirrors. The capability of producing high Q values makes the WGM resonators useful for optical modulation and other optical processes.